Removal of non-condensable gases from a closed loop process

ABSTRACT

A method which allows the ejection of non-condensable gases, notably air, from a closed loop power generation process or heat pump system, is disclosed. A vessel in which a working fluid is absorbed or condensed can be separated from the power generation processes by valves. Residual gas comprising C02, non-condensable gas such as air, water and alkaline materials including amines may be compressed by raising the liquid level in said vessel. The concurrent pressure increase leads to the selective absorption of C02 by alkaline materials. In simpler embodiments, mainly air is removed from one- or two-component processes. Following the compression, non-condensable gas may be vented, optionally through a filter. The method is simple and economic as vacuum pumps may be omitted. The method is useful for any power generation and Rankine cycle, and particularly useful for the power generation process known as C3 or Carbon Carrier Cycle.

FIELD OF THE INVENTION

This invention relates to removal of non-condensable gases from closedloop processes especially in the field of power generation.

DEFINITIONS

Non-condensable gas: air including oxygen, nitrogen and argon, carbondioxide (CO2); closed-loop power generation process: Rankine cycle,Organic Rankine cycle, ORC, Carbon Carrier

Cycle, heat pump system involving compression/heating andexpansion/cooling of a working fluid; vacuum: system pressure below 1bar. In the text, a term such as CO2 or air may denote anynon-condensable gas or mixture thereof.

BACKGROUND AND PRIOR ART

Accumulation of undesired gases is a known problem in fields such aschemical engineering and power plant operation. Gas, notably air, leaksinto equipment not only operated under vacuum but even into processesoperated above atmospheric pressure.

In water-steam based power plants, tray- or spray-based deaerators areused to remove air, see “deaerator” e.g. in Wikipedia. Gas removal fromwater is affected by making use of Henry's law, i.e. reduced gassolubility at low partial pressure, and the principle that gassolubility is reduced at higher temperatures (see e.g.www.sterlingdearator.com). Also, chemicals such as sodium sulphite canbe employed as oxygen scavengers.

Numerous disclosures describe solutions of associated problems,including EP 1 829 594 (Asahi, 2004) for chemical processes, U.S. Pat.No. 4,026,111 (DOW, 1976) for removal of gas from brine for geothermalenergy generation, U.S. Pat. No. 4,905,474 (steam condenserapplication), U.S. Pat. No. 7,588,631 (2006, vacuum deaeration bycyclones), and JP 2006 125 775 (Sanyo Electric, inventor Omori Mitsunoriet al) which describes a vacuum pump solution ejecting non-condensablegases from a water/LiBr/octanol based refrigeration machine.

US 2002 000 7732 discloses membrane based separation of a working fluidin power generation from non-condensable gas.

WO 95/27 985 (Pennsylvania Power&Light Company) discusses varioussolutions attempted in the boiling water reactor industry, see pp. 10chapter c.

Relevant for this invention is U.S. Pat. No. 5,487,765 (Ormat, 1994)which discloses a separate vessel comprising a membrane or diaphragmthrough which non-condensable gases diffuse but which retains workingfluids such as lower paraffins. This solution is highly useful in an ORCprocess (Organic Rankine Cycle) in which a working fluid such as butaneor pentane (or HCFC) is evaporated at high temperatures and condensed atlower temperature. The pressure difference between the high and lowtemperature sections is used to operate a turbine for electricitygeneration.

In energy-generation processes operated partly under vacuum, the risk ofair ingress is obviously higher. The C3 process as disclosed in WO2012/128 715 comprises a CO2 gas loop driving a turbine whereby the CO2gas is absorbed temporarily in the cold section of the process by e.g.amines and released from said amines at higher temperatures. The processresults in a thermodynamic cycle operated between e.g. 2-3 bar on thehigh pressure side and 0.1-0.3 bar on the low pressure side, giving ahigh pressure quote and a high heat-to-electricity efficiency. In thisprocess, air ingress on the vacuum side reduces the pressure quote.Therefore, air or other non-condensable gases have to be removed fromthe process. At the same time, volatile amines shall not be ejected fromthe process.

Further to the problems not solved by prior art, pumping out residualgas, whether directly from the absorber or condenser or from a separatedvessel, leads to unacceptably high removal of especially volatileworking fluids, including CO2, amines, and solvents such as acetone.Therefore, a solution is desired which allows the removal ofair/non-condensable gas partly at higher pressure than prevailing in theabsorber section, this in order to increase the condensation of volatileworking fluid, partly at lower temperature than prevailing in theabsorber section, also in order to favour condensation of working fluid,and partly at minimum costs, i.e. with minimum or no investment costsespecially for vacuum pumps.

Some modifications and specific embodiments of the C3 process aredisclosed in documents mentioned below, all of which are included byreference.

BRIEF DESCRIPTION OF THE INVENTION

A vessel in which e.g. CO2 working fluid is absorbed is separated byvalves from a power generation process, in particular C3 as described inWO 2012/128 715 and SE 2013/051 059, SE 1300 576-4, SE 1400 027-7 and SE1400 160-6, hereby incorporated by reference, but also standard ORCsolutions based on one or more volatile working fluids such as lowerparaffins, classic refrigerants and in general ORC working fluids withboiling points at atmospheric pressure below 100° C. In standardoperation, said vessel may function as absorption chamber where CO2 gasis absorbed by amines. During an ejection cycle for non-condensable gas,residual gas comprising CO2, non-condensable gas, water and alkalinematerials including amines may be compressed by raising the liquid levelin said vessel. The concurrent pressure increase leads to the selectiveabsorption of CO2 by alkaline materials. In this way, the concentrationof volatile amines in the gas space is reduced. Following thecompression to above atmospheric pressure, non-condensable gas may bevented, optionally through a filter or a membrane in order to absorbremaining volatile amine. Optionally, a membrane or diaphragm may beused separating said vessel into two sections. Said membrane ispermeable for air, but impermeable for volatile amines. Ideally, themembrane is not very permeable for CO2 gas. The membrane is ideally notin contact with liquid amine. Remaining or condensing liquid amine maybe transferred back to the vessel, also without using a pump. The methodis simple and economic as vacuum pumps may be omitted. However, using avacuum pump is also considered an option for faster removal ofnon-condensable gases.

DESCRIPTION OF THE FIGURE

The invention will now be described by way of non-limiting examples withreference to the accompanying drawing, in which

FIG. 1 is a schematic drawing of an arrangement highly suitable for theremoval of at least one gas from a closed loop process involving one ortwo working fluids which are condensed rather than chemically absorbed,further showing how the gas removal unit is integrated into the completepower generation process.

EMBODIMENTS OF THE INVENTION

This invention concerns in one aspect a method or procedure for theremoval of at least one non-condensable gas from thermodynamic cycles,particularly from the C3 process mentioned above, which operates partlyunder vacuum, or ORC processes operating partly under vacuum.

In one embodiment, the working fluid may comprise a low boiling solventsuch as methanol, ethanol, acetone, isopropanol or butanol on the onehand at a concentration of at least 5% by weight, and ammonia as well asamines including diethylamine, dipropylamine, dibutylamine, andwater-soluble amines including MEA, in water or organic solvents, suchas disclosed in above mentioned documents and CO2. The proceduresdescribed below are suitable for the automatic and controlled removalair while the power generation cycle is in operation. Pressurizing leadsto condensation of condensable gases, such as the solvents mentionedabove. Despite this pressurizing step, a certain loss of volatilesolvent or amine or CO2 is difficult to avoid but acceptable.Optionally, condensable components can be trapped outside the cycle bymeans known in the art, such that emissions to the environment areavoided.

In a further aspect, now referring to FIG. 1, an absorption orcondensation vessel 7 is in connection with a main absorbing orcondensing vessel 50 through a valve 2 and a valve 4. Air removal isachieved in batch operation using the following sequence:

A) A valve 3 is opened to equilibrate the pressure in the condensationvessel 7 and the main condensing vessel 50, while valves 2, 4 and 5 areclosed. Condensed working fluid is drained through a line 19 into themain condensing vessel 50, prior to a pump 51. Optionally, a pump 24 isemployed for working fluid transfer, e.g. if vessel 7 cannot be emptiedby gravity.

B) The valve 4 is opened to start the spraying of cold condensed workingfluid supplied through a line 16. The valve 2 is opened to allow ingressof gas through a line 18 from the main condensing vessel 50 which inturn receives gas from turbine 53. Pressures and temperatures aremeasured by sensors T8 and T9 and T10 as well as P12 and P14.

C) Working fluid condensation leads to a temperature increase,proportional to the condensation enthalpy of the working fluid andproportional to the amount of condensing working fluid. This temperatureincrease is lower in the condensation vessel 7 than in main condensingvessel 50 partly due to the presence of accumulating non-condensablegases, and partly due to the fact that a higher liquid reflux ratio isused. As the batch sequence progresses, the temperature in thecondensation vessel 7 may be 2-4° C. lower than in main condensingvessel 50 for a situation where 90/20° C. water is used forheating/cooling. The temperature difference T8-T9 should be around30-700 of the corresponding difference T8-T10. If T8-T9 is approachinglower values (<30% of T8-T10), this may be taken as practical indicationthat no more gaseous working fluid is condensed in the condensationvessel 7. (Note that the given percentage levels are indicative only.)At that stage, the valves 2 and 3 are closed whereas the valve 4 remainsopen such that working fluid supply through the supply line 16continues. Part of the remaining gaseous working fluid is condensed dueto continued liquid flow and compression of the gas space which is nowisolated, and the liquid level in the condensation vessel 7 rises. Afurther pump 13 may be provided for manipulating the absorption liquidlevel in said at least one absorption or condensation chamber 7.

D) The valve 4 is closed as soon as the pressure P12 in the condensationvessel 7 is close to or equal to the liquid pressure P11 in the supplyline 16 from a cooler 54.

E) The valve 5 is opened such that a pump 20 can supply liquid to thecondensation vessel 7. The concurrent pressure increase leads to furthercondensation of gaseous working fluid.

F) As the pressure in the condensation vessel 7 is approaching thepressure P14 in a supply line 17 which in turn is fed from the supplyline 16, the valve 1 is opened to release non-condensable gas throughoptional secondary vessel 22, optional valve 21 and vent line 23. Vessel22 may serve as collection or recovery vessel for solvent if required.It is intended to eject as much air as possible, therefore, as atechnical option, liquid supply through supply line 17 and valve 5 cancontinue until the liquid level in the condensation vessel 7 reaches aspecified level. Ejection of liquid can be prevented by known methods,e.g. a floating device (not shown in FIG. 1) which blocks the valve 1 ifthe liquid level is at the maximum level. Diaphragms or membranesessentially impermeable to gases other than oxygen, nitrogen and argonare used e.g. in said secondary vessel 22 to avoid the loss of processgas, notably CO2 and volatile solvent and amine.

G) Step A is repeated.

At a starting time of release of non-condensable gas(es) from said atleast one absorption or condensation chamber 7, the pressure in said atleast one absorption or condensation chamber is at least 10%, preferablyat least 30%, more preferably at least 80%, and most preferably even150% higher than the pressure in a main absorption or condensationvessel (50).

In the embodiment described above, it appears that the driving forceenabling gas separation and subsequent ejection from the closed loopprocess is the temperature difference between (one or more) condensationvessel(s) 7 and the main absorption or condensation vessel(s) 50. Thistemperature difference is caused by the fact that liquid working fluidis pumped into the condensation vessel 7 at a higher rate, relative tothe flow rate of gaseous working fluid, than into the main absorptionvessel 50. Therefore the liquid in the condensation vessel 7 isgenerally colder than in the main absorption vessel 50. Gaseous workingfluid and non-condensable gas is entering the condensation vessel 7. Thecondensation of main working fluid leads to the enrichment ofnon-condensable gas in a gas space 6 which further causes thetemperature to drop in the condensation vessel 7. At a certain stage, itis practical to start sequence (C) described above.

As described, the fact that liquid in the condensation vessel 7 iscolder than at any other stage in the process, is driving the gasseparation. Cooling may be affected by the higher liquid flow rate, oralternatively by active cooling. The former method is using less energy,the latter method may be chosen in embodiments where e.g. spacerequirements dictate so.

Referring further to FIG. 1, also the complete closed-loop process isshown, here as a simple Rankine process with a heat exchanger 52 forgeneration of hot gaseous working fluid, a turbine 53, the maincondensation vessel 50, the temperature sensor T10 and a working mediumpump 51. It should be appreciated that working fluid exiting from heatexchanger/absorber/condenser 50 i.e. the main absorption vessel 50 canbe partly recycled to the top of the same, e.g. to achieve a loweraverage temperature in said main absorption vessel 50 or to aidabsorption in the main absorption vessel 50.

In one of the preferred embodiments, acetone is used as working fluid.The solubilities of resp. oxygen and nitrogen are very low in acetone(see Battino, J.Phys.Chem.Ref.Data Vol 12, No.2, 1983, p. 174 and Vol.13, No. 2, p. 587) such that air removal from acetone even at lowtemperature (e.g. between 20-40° C. is efficient. Compared to prior-artsolutions, loss of acetone or working fluid is significantly reduced.

In one embodiment, the gas mixture ejected from the process, comprisingnon-condensable gas(es) and minor amounts of solvents including acetone,isopropanol, amines or the like is prevented from entering theenvironment by use of a cold trap, suitable filters such as carbonblack, zeolites or other absorbents, a scrubber or a burning/flaringunit.

In one embodiment, removal of non-condensable gases may be automaticallycontrolled e.g. by a software, whereby gas removal is triggered by oneor more process sensor (T8, T9, T10 and P11, P12 and P14) indicatingingress or presence of non-condensable gas, specifically usingtemperature and pressure sensors (T8, T9, T10 and P11, P12 and P14),directly or indirectly indicating presence of non-condensable gas.

The method described is also useful for air removal from a) steam-basedRankine cycles partly under vacuum but also from b) high pressure ORCsystems. In case a) the method would be used to save costs, e.g. for avacuum pump, in case b) this is relevant because already low airconcentrations deteriorate the performance of heat exchangers such ascondensors for ORC working fluids. Air ingress cannot be excludeddespite the use of higher than atmospheric pressures.

In a different embodiment, the technique for gas removal described aboveis used in a heat pump system. Essentially, in a heat pump a separategas compression step is used to generate higher temperatures, e.g. forhouse heating purposes, from low value heat sources. Suitable heat pumpdesigns operating partly under vacuum are disclosed in SE 1300576-4assigned to Climeon AB and related disclosures.

It should be understood that above embodiments are merely examples ofuseful sequences to achieve the objective of the invention, namely toremove non-condensable gases from a closed loop process representing athermodynamic cycle, specifically the C3 cycle or any Rankine cycleoperating partly under vacuum.

Similar arrangements should be seen as falling under the spirit of thisinvention. In particular, diaphragms or membranes may be included tofurther reduce the loss of volatile materials such as amines, however,such solutions will be used depending on costs/benefits calculations.

In summary, a simple solution is disclosed for removal ofnon-condensable gases from closed-loop-processes. The solution is cheapin construction and operation, and can be operated at any time while thethermodynamic cycle is operated, i.e. no stand-still is required.

The methods disclosed here can be used in combination with closed-loopprocesses comprising working gas and chemicals as temporary andreversible working gas absorption agents. Specifically, the methods canbe used combination with the C3 thermodynamic cycle comprising CO2 asworking gas and amines as temporary and reversible CO2 absorptionagents. Further use is possible in combination with a thermodynamiccycle comprising paraffins such as propane, butane, pentane, hexane, andits isomers, alcohols such as methanol, ethanol, isopropanol, butanol orketones such as acetone or refrigerants e.g. containing fluorine atomsor water as working gas at a concentration of at least 10% by weight.

Finally, the methods can be used in combination with a heat pump orrefrigeration system, preferably operating partly under vacuum.

1-12. (canceled)
 13. A method for the removal of non-condensable gasesfrom a system using a closed-loop thermodynamic cycle and wherein saidsystem comprises a main absorption/condensation vessel used forabsorbing or condensation of a working fluid, the mainabsorption/condensation vessel is adapted to be connected to a gasremoval unit comprising a secondary absorption/condensation vessel usedfor absorbing or condensation of the working fluid during gas removal,lines and valves adapted to selectively connect the secondaryabsorption/condensation vessel to the main absorption/condensationvessel, and a vent line connected to the secondaryabsorption/condensation vessel via a vent valve, said method comprisingthe steps of: on a repeated batch basis: filling the secondaryabsorption/condensation vessel with condensed working fluid, condensablegaseous working fluid, and non-condensable gas(es) from the mainabsorption/condensation vessel, raising a working fluid level in thesecondary absorption/condensation vessel by spraying of working fluidfrom the main absorption/condensation vessel into the secondaryabsorption/condensation vessel such that condensable gas(s) in thesecondary absorption/condensation vessel condenses and the gas pressurein the secondary absorption/condensation vessel increases, and releasingnon-condensable gas(es) from the secondary absorption/condensationvessel through the vent line, wherein at a starting time of release ofsaid non-condensable gas(es)from the secondary absorption/condensationvessel, a pressure in the secondary absorption/condensation vessel is atleast 10% higher than the pressure in the absorption/condensationvessel.
 14. The method according to claim 13, wherein in the releasingexcess gas(es) step, at a starting time of release of saidnon-condensable gas(es)from the secondary absorption/condensationvessel, a pressure in the secondary absorption/condensation vessel is atleast 80% higher than the pressure in the absorption/condensationvessel.
 15. The method according to claim 13, wherein in the releasingexcess gas(es) step, at a starting time of release of saidnon-condensable gas(es)from the secondary absorption/condensationvessel, a pressure in the secondary absorption/condensation vessel is atleast 150% higher than the pressure in the absorption/condensationvessel.
 16. The method according to claim 13, further comprisingselecting the closed-loop thermodynamic cycle from the group consistingof: (1) a Rankine cycle using steam or solvents selected from the groupof water, alcohols, ketones, esters, paraffins and fluorinated solvents,(2) a Carbon carrier thermodynamic cycle, and (3) an organic Rankinecycle operating at least partly under vacuum.
 17. The method accordingto claim 13, comprising the step of manipulating the working fluid levelin the secondary absorption/condensation vessel so that the temperatureof a condensed working fluid is lower in the secondaryabsorption/condensation vessel than in the main absorption/condensationvessel.
 18. The method according to claim 13, further comprising:fluidly coupling the main absorption/condensation vessel and thesecondary absorption/condensation vessel with pumps and pipes, andmonitoring, using temperature and pressure sensors, (1) working fluidpressure and temperature before entering the secondaryabsorption/condensation vessel, and (2) working fluid temperature withinthe secondary absorption/condensation vessel, wherein the step ofraising the working fluid level in the secondary absorption/condensationvessel is performed by said pumps based on temperatures and pressuresmeasured by said temperature and pressure sensors.
 19. The methodaccording to claim 13, wherein releasing the non-condensable gas fromthe absorption/condensation vessel comprises passing the non-condensablegas through at least one of a diaphragm or a membrane essentiallyimpermeable to gases other than oxygen, nitrogen and argon.
 20. Themethod according to claim 13, wherein the releasing step comprisespassing the excess gas(es)through at least one of a cold trap, a filter,a gas scrubber, and a burning/flaring unit.
 21. The method according toclaim 13, further comprising triggering the removal of non-condensablegases based on information from a temperature sensor and a pressuresensor indicating the presence of non-condensable gas.
 22. The methodaccording to claim 13, wherein the working fluid comprises working gasand chemicals, the chemicals acting as temporary and reversible workinggas absorption agents.
 23. The method according to claim 13, wherein theclosed-loop thermodynamic cycle is a carbon carrier thermodynamic cyclein which the working fluid comprises CO₂ as working gas and amines astemporary and reversible CO₂ absorption agents.
 24. The method accordingto claim 13, in which the working fluid comprises one or more of:paraffins including propane, butane, pentane, hexane, and isomersthereof; alcohols including methanol, ethanol, isopropanol, butanol;ketones including acetone; and refrigerants containing at least one offluorine atoms and water as a working gas.
 25. The method according toclaim 13, wherein the closed-loop thermodynamic cycle involvescompression or heating and expansion or cooling of a working fluid andwherein the main absorption/condensation vessel is used for absorbing orcondensation of the compressed or heated working fluid.
 26. The methodaccording to claim 25 in combination with a chosen one of a heat pumpand a refrigeration system.
 27. The method according to claim 26,wherein the chosen one of a heat pump and a refrigeration systemoperates partly under vacuum.
 28. The method according to claim 13 incombination with a chosen one of a heat pump and a refrigeration system.29. The method according to claim 28, wherein the chosen one of a heatpump and a refrigeration system operates partly under vacuum.
 30. A gasremoval unit, for use with a closed-loop thermodynamic cycle systemcomprising a main absorption/condensation vessel for absorbing orcondensation of a working fluid, the gas removal unit comprising: asecondary absorption/condensation vessel; a working fluid deliverystructure for selectively spraying working fluid from the mainabsorption/condensation vessel into the secondaryabsorption/condensation vessel; gas delivery structure for delivery ofcondensable and non-condensable gas(es) from the closed-loopthermodynamic cycle system into the secondary absorption/condensationvessel; and vent line structure selectively coupling the secondaryabsorption/condensation vessel to a gas venting region; whereby thesecondary absorption/condensation vessel can be filled with the workingfluid and condensable and non-condensable gas(es), such that (1)condensable gas(es) in the secondary absorption/condensation vesselcondense, (2) a gas pressure in the secondary absorption/condensationvessel increases, and (3) non-condensable gas(es) can be released fromthe secondary absorption/condensation vessel through the vent linestructure.
 31. The gas removal unit according to claim 30, wherein: theworking fluid delivery structure comprises a pump, a working fluid line,and a working fluid valve along the working fluid line, selectivelyfluidly connecting the main and secondary absorption/condensationvessels; and the gas delivery structure comprises a gas line and gasvalve along the gas line.
 32. The gas removal unit according to claim30, wherein: the closed-loop thermodynamic cycle system involvescompression or heating and expansion or cooling of the working fluid;and the main absorption/condensation vessel comprises a mainabsorption/condensation vessel for absorbing or condensation of thecompressed or heated working fluid.
 33. The gas removal unit accordingto claim 32, wherein the closed-loop thermodynamic cycle comprises achosen one of a heat pump and a refrigeration system.
 34. The gasremoval unit according to claim 30, wherein the closed-loopthermodynamic cycle is one of the following: (1) a Rankine cycle usingsteam or solvents selected from the group of water, alcohols, ketones,esters, paraffins and fluorinated solvents, (2) a Carbon carrierthermodynamic cycle, and (3) an organic Rankine cycle operating at leastpartly under vacuum.
 35. The gas removal unit according to claim 30wherein the gas removal unit comprises: temperature and pressure sensorsto monitor, (1) working fluid pressure and temperature before enteringthe secondary absorption/condensation vessel, and (2) working fluidtemperature within the secondary absorption/condensation vessel, for useby the working fluid delivery structure and the gas delivery structure.36. The gas removal unit according to claim 30, wherein the vent linestructure comprises at least one of a diaphragm or a membrane, which isessentially impermeable to gases other than oxygen, nitrogen and argon.37. The gas removal unit according to claim 30, wherein the vent linestructure comprises at least one of a cold trap, a filter, a gasscrubber, and a burning/flaring unit.
 38. The gas removal unit accordingto claim 30, wherein the closed-loop thermodynamic cycle is a carboncarrier thermodynamic cycle in which the working fluid comprises CO2 asworking gas and amines as temporary and reversible CO2 absorptionagents.
 39. The gas removal unit according to claim 30, in which theworking fluid comprises one or more of: paraffins including propane,butane, pentane, hexane, and isomers thereof; alcohols includingmethanol, ethanol, isopropanol, butanol; ketones including acetone; andrefrigerants containing at least one of fluorine atoms and water as aworking gas.
 40. A non-condensable gas(es) removal system comprising: aclosed-loop thermodynamic cycle system comprising a mainabsorption/condensation vessel for absorbing or condensation of aworking fluid; and a gas removal unit comprising: a secondaryabsorption/condensation vessel; a working fluid delivery structure,comprising a pump, a working fluid line, and a working fluid valve alongthe working fluid line, selectively fluidly connecting the main andsecondary absorption/condensation vessels, for selectively sprayingworking fluid from the main absorption/condensation vessel into thesecondary absorption/condensation vessel; gas delivery structure,comprising a gas line and a gas valve along the gas line, for deliveryof condensable and non-condensable gas(es) from the closed-loopthermodynamic cycle system into the secondary absorption/condensationvessel; and vent line structure selectively coupling the secondaryabsorption/condensation vessel to a gas venting region; whereby thesecondary absorption/condensation vessel can be filled with the workingfluid and condensable and non-condensable gas(es), such that (1)condensable gas(es) in the secondary absorption/condensation vesselcondense, (2) a gas pressure in the secondary absorption/condensationvessel increases, and (3) non-condensable gas(es) can be released fromthe secondary absorption/condensation vessel through the vent linestructure.